Design Schemes of Main Piers of a Railway-Crossing Rigid-Frame Bridge with Integrally-Rotated Two Superstructures
The main bridge of Changli Bridge carrying a section of Guangxi Binhai Highway is a continuous rigid-frame bridge with two equal spans of 79 m.With a deck width of 39.4 m,the bridge has double superstructures that consist of three-cell box girders,the left and right superstructures share the 5.22 m-high,box-type,double-thin-walled piers(with extra cap beams compared with traditional double-thin-walled piers).The two superstructures were cast in situ on scaffolds parallel the railway,and then integrally rotated to span over the railways,using a spherical hinge that measured 6.0 m,and the weight of the rotated structures reached 36 000 t.Given the characteristics of the bridge,three types of piers,including the double-thin-walled piers,wall piers and hollow box piers,were recommended and compared from aspects of structural configuration,load bearing behavior and thrust stiffness,and the double-thin-walled piers were finally selected,which was considered the best solution to accommodate the characteristics of the bridge,specifically the low piers,wide deck,long cantilevers of the rigid T frame,massive rotation tonnage and heavy-loaded pile caps.The double-thin-walled piers exhibit great flexural stiffness,which is beneficial to improve the safety of the structure at the long-cantilever rotation stage and alleviate the peaks of negative bending moments of the superstructures at the main piers,due to the small thrust stiffness,the stiffness ratios of the piers and superstructures are relatively reduced,and the load bearing conditions of the two get improved.To further reduce the thickness and enhance the loaded condition of the pile cap restricted by the short pier column,separated left and right superstructures and the spherical hinge,the double-thin-walled piers are fitted with extra prestressed concrete cap beams on top of the thin walls,becoming box structures that are different from the traditional double-thin-walled piers,as a result,the pile caps are made thinner,the stresses in the main piers and the pile caps are remarkably reduced,and the load bearing performance of the bridge is better.
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